Sea floor mineral deposits are common in northern Baltic Sea

A study recently completed at the University of Helsinki indicates that there are large numbers of mineral concretions containing valuable metals on the seafloor of Finnish marine areas, holding both commercial and conservational value.

Despite their prevalence in the Baltic Sea, very little is known about these mineral deposits.  

“In spite of their numerousness, surprisingly little research has been carried out on them, and there is only fragmented knowledge of their numbers and distribution,” says doctoral student Laura Kaikkonen from the Faculty of Biological and Environmental Sciences. In her doctoral research, Kaikkonen is investigating these mineral deposits found on the seafloor and the environmental impacts of their potential utilisation.  

In the recent assessment of threatened habitat types in Finland, the concretion fields of the Baltic Sea have in fact been declared as a data-deficient habitat type.  

Mineral concretions containing iron, manganese, phosphorus and rare earth metals occur not only on the ocean floor, but also in more shallow marine regions, including the Baltic Sea. In great numbers, such deposits can cover the seafloor almost entirely, and on soft seafloors they provide a hard substrate on an otherwise unstable sedimentary surface, potentially forming a separate habitat from the surrounding seafloor to organisms living on the seabed.  

A study recently completed in collaboration between the University of Helsinki, the Geological Survey of Finland and the  Finnish Environment Institute demonstrates that seafloor mineral deposits with a high concentration of iron and manganese occur in at least 11% and, at the most, 20% of Finnish marine areas.  Earlier, the deposits were thought to be found in abundance only in deeper waters, but Kaikkonen and her co-authors have shown that a surprising amount of deposits also occur in the immediate vicinity of the coast.  

The study utilised observations of seafloor characteristics collected from more than 140,000 sampling points under the Finnish Inventory Programme for the Underwater Marine Environment (VELMU).  

“Looking into the distribution of seafloor mineral concretions helps us understand their role in marine ecosystems, which makes it possible to rely on research-based knowledge when making decisions on their potential conservation,” Kaikkonen says. 

Commercial potential  

Due to containing high concentrations of manganese and rare earth metals, investigations on the commercial extraction of mineral deposits have been made in the Pacific Ocean and other deeper marine areas. The same issue is also being considered regarding the Baltic Sea. On the Russian side of the Gulf of Finland, experiments with mineral concretion extraction have already been carried out.  Due to the lack of knowledge on concretion fields, the long-term environmental effects of their utilisation remain uncertain for the time being.  

“Unrestricted extraction may have long-term effects on the functioning of the marine ecosystem, something which has to be investigated before commercial activity becomes topical,” Kaikkonen notes. 
In summer 2019, fieldwork was initiated under the same project where the biodiversity of concretion fields in relation to naked seafloors is investigated by diving and collecting sediment samples. The work has been carried out in collaboration with the Finnish Environment Institute and the Geological Survey of Finland as part of the SmartSea project of the Strategic Research Council of the Academy of Finland as well as the MERISAMPO project funded by the Ministry of the Environment. 

Original article 

The study was published in the Frontiers in Marine Science journal: 
Kaikkonen, L., Virtanen, E. A., Kostamo, K., Lappalainen, J., & Kotilainen, A. T. (2019). Extensive coverage of marine mineral concretions revealed in shallow shelf sea areas. Frontiers in Marine Science, 6, 541. DOI: 10.3389/fmars.2019.00541